1. Field of the Invention
The present invention relates to methods and apparatuses for lifting and handling of concrete elements, examples of such are bridge beam and deck elements, slabs, piles, wall panels, concrete legs and floating concrete caisson structures of oil platforms, prestressed concrete structures in general and the like. In particular, the lifting and handling of concrete elements up to and greater than 1,000 tonnes (t). The invention may be applied to concrete elements as commonly found in the building, construction, concrete pre-casting, demolition and emergency rescue industries/application areas.
2. Description of the Art
Lifting and handling of concrete elements is typically done by use of a crane or other lifting machine which is connected via a rigging to one or a number of lifting inserts permanently embedded in the concrete element to be lifted. Examples of such lifting inserts/anchors are U.S. Pat. Nos. 4,000,591, 4,367,892, 4,386,486, 4,437,642 and 4,580,378. In addition protruding loops of cable, wire loop and reinforcing bar have also been used to provide a lifting insert/anchor for attachment. The crane rigging may attach to the lifting insert via (for example) a lifting clutch, shackle, hook, lifting eye or any suitable attachment means or combination of.
However permanently embedded lifting inserts must be suitably protected against corrosion in order that the integrity of the concrete element is maintained and/or if the lifting insert is to have some re-use. In addition lifting inserts are a significant cost factor in the manufacture and use of concrete elements.
One example of extensive use of lifting inserts/anchors is in the pre-cast manufacture of panels, slabs and pre-stressed bridge beams where the lifting inserts are embedded during the casting process. Once the concrete element has been cast in a pre-caster facility then the lifting inserts are used to lift the concrete element from the floor or from the moulding/casting form in which it is made. The concrete element panels are then typically placed on racks or stacked to allow the concrete to gain strength prior to being delivered to a construction site. The delivery to the construction site requires a lift onto a transporter and then a subsequent lifting and handling to position the concrete element in the construction project. The embedded lifting inserts remain in the concrete element and are of no further use.
If the concrete element is made by a tilt slab builder on the building construction site then the lifting inserts are often used in a single lift of the concrete element from the position in which it was cast into its final position in a building project. Again, the embedded inserts remain in the concrete element and are of no further use.
For lifting inserts typically used in concrete element manufacture the corrosion protection process has particular dangers if not properly treated, due to hydrogen embrittlement of a steel lifting insert, for example. Lifting inserts that are embrittled may unexpectedly fail during a lift of a concrete element, endangering workers in the proximity of the load. As a consequence, the use of expensive redundant permanent inserts and their attendant safety issues is a significant cost and risk to the building and construction industry.
Portable concrete road barriers often feature steel lifting inserts which are used to lift the road barriers numerous times over the course of their many years of use. The lifting inserts embedded in the upper faces of concrete road barriers are exposed to the elements which may promote corrosion and consequently affect the serviceability of the lifting insert over its service life.
Expansion bolts, screw fasteners and the like that may be used to secure items or structures to a concrete element are not suitable for the lifting and handling of concrete elements. Expansion bolts/fasteners are not suited for the weight of concrete elements and the dynamic tensile and shear loads experienced in their lifting and handling. Such systems as expansion bolts/fasteners at large dynamic loads of some tonnes may be prone to failure, for example, via thread stripping, inadequate pull-out cone and/or the expanding anchor fails. National standards for lifting and handling of concrete elements typically do not allow for the use of expansion screw bolts. In addition expansion bolts are typically not completely removable and designed for single use; the screw or bolt may be removed but the expanding anchor remains behind in the hole to corrode and prevent re-use of the hole.
None of these prior art devices and methods provides an entirely satisfactory solution to the provision of lifting and handling of concrete elements, nor to the ease of use and verification of a safe lifting operation.